Adie syndrome

Disease class: Autonomic nervous system diseases

Also known as

• Holmes-Adie syndrome

 

Signs and symptoms

• A tonically dilated pupil
• Pupil reacts slowly to light but shows a more definite response to accommodation (i.e., light-near dissociation)

Complex regional pain syndromes

Disease class: Autonomic nervous system diseases

 

Horner syndrome

Disease class: Autonomic nervous system diseases

 

Cranial Nerve VI: Abducens Nerve

Organ system: The cranial nerves

Function

Motor

• Carries motor signals to the lateral rectus muscle. This is an extraocular muscle which draws the pupil of the eye outwards.

Cranial Nerve XII: Hypoglossal Nerve

Organ system: The cranial nerves

Function

Motor

• Carries motor signals to the extrinsic and intrinsic muscles of the tongue, with the exception of palatoglossus (innervated by the vagus nerve).
• Motor output during swallowing (alongside CN-IX and CN-X).

Cranial Nerve XI: Accessory Nerve

Organ system: The cranial nerves

Function

Motor

• Carries motor signals to the sternocleidomastoid muscles. This can turn rotate the head outwards.
• Carries motor signals to the trapezius muscles. This can elevate the pectoral girdle.

Cranial Nerve IV: Trochlear Nerve

Organ system: The cranial nerves

Function

Motor

• Carries motor signals to the superior oblique muscle. This is an extraocular muscle which draws the pupil of the eye downwards and rotates it outwards.

Cranial Nerve 0: Terminal Nerve

Organ system: The cranial nerves

Functions

Sensory

• Pheremone sensation during kissing or physical closeness
• Encouraging pair bonding between compatible healthy mates

Notes

• The existence of this cranial nerve is undisputed in various non-human species. In humans it is not universally recognised and it is poorly understood.
• It is possible that this structure is non-functional and vestigial. This could have atrophied alongside the olfactory system during human evolution. It could have been made redundant by the development of high intelligence and complex social behaviours.
• One reason for the lack of consesus is the difficulty in preserving and identifying this small structure during dissection.

 

See also

• Cranial Nerve I: Olfactory Nerve

Cranial Nerve VII: Facial Nerve

Organ system: The cranial nerves

Functions

Sensory

• Carrying taste sensation from the anterior 2/3 of tongue.

Motor

• Carrying motor signals to the muscles of facial expression 

 

Pathology

• Facial nerve diseases

Cranial Nerve IX: Glossopharyngeal Nerve

Organ system: The cranial nerves

Functions

Sensory

• Carrying taste sensation from the posterior 1/3 of tongue.   

Motor

• Motor output during swallowing (alongside CN-X and CN-XII).

Parasympathetic nervous system

Organ system: Autonomic nervous system

Function

• "Rest and digest"
• To reduce heart rate and stroke volume
• To dilate the capillaries, reduce peripheral vascular resistance, and decrease blood pressure
• To reduce respiratory rate
• To constrict the pupils (less light enters the retina)
• To promote gastrointestinal activity
• To initiate penile erection or vaginal tumescence

 

Mediators

• Cranial nerves: CN X (The vagus nerve)
• Spinal nerves: The pelvic splanchnic plexus

Sympathetic nervous system

Organ system: Autonomic nervous system

Function

• "Fight or flight"
• To increase heart rate and stroke volume
• To constrict the capillaries, raise peripheral vascular resistance and blood pressure
• To increase respiratory rate
• To inhibit gastrointestinal activity
• To dilate the pupils (more light enters the retina)
• To initiate ejaculation and orgasm

Somatic nervous system

 Organ system: Peripheral nervous system

Definition: The component of the peripheral nervous system which mediates transmission of information between the conscious mind and the body.

 

Functions

• Sensation of the external and internal enviroments and conscious perception of these sensations.
• Transmission of output from the central nervous system (e.g. voluntary motor commands) to the effector tissues (e.g. muscles)

Pathology 

• Paralysis
• Mononeuropathy
• Polyneuropathy
• Radiculopathy
• Allodynia
• Chronic pain
• Somatoform disorders

Autonomic nervous system

 Organ system: Peripheral nervous system

Definition: The component of the peripheral nervous system which carries involuntary, subconscious commands to the muscles and sweat glands of the body.

 

Divisions

By function

• Sympathetic nervous system
• Parasympathetic nervous system

By origin

• Cranial nerves
• Spinal nerves

The sympathetic and parasympathetic nerves are constantly transmitting signals (known as "sympathetic tone", "vagal tone", etc.) to maintain a dynamic balance in their target tissues. This 'tug of war' shifts towards sympathetic or parasympathetic effects as necessary.

Pathology

• Autonomic nervous system diseases

Removal of one system leaves the other system completely unopposed. For this reason, patients with spinal injuries may develop "autonomic dysfunction". Normal stimulation of the remaining system can cause life-threatening effects.

The spinal nerves

 Organ system: Peripheral nervous system

Features

• The spinal nerves originate from segments of the spinal cord.
• There is a pair of spinal nerve roots at each level in the vertebral column.

 

Cervical nerves

There are 7 cervical vertebrae in the spine.
Each spinal nerve pair arises above a cervical vertebra except C8, which arises below cervical vertebra C7.

• C1
• C2
• C3
• C4
• C5
• C6
• C7
• C8

 

Thoracic nerves

There are 12 thoracic vertebrae in the spine. 
Each spinal nerve pair arises below a thoracic vertebra.

• T1
• T2
• T3
• T4
• T5
• T6
• T7
• T8
• T9
• T10
• T11
• T12

 

Lumbar nerves

There are 5 lumbar vertebrae in the spine.
Each spinal nerve pair arises below a lumbar vertebra.

• L1
• L2
• L3
• L4
• L5

 

Sacral nerves

Along the sacrum the spinal nerve pairs arise through sacral foramina.

• S1
• S2
• S3
• S4
• S5

 

Coccygeal nerves

The final pair of spinal nerves are the coccygeal nerves.

• Co1

Compare with

• Cranial nerves

The cranial nerves

 Organ system: Peripheral nervous system

Features

• There are 12 well-known cranial nerves and 1 disputed cranial nerve (CN-0).
• The cranial nerves exist in symmetrical pairs.
• CN-0, CN-I, CN-II arise from the brain.
• CN-III to CN-XII (ten cranial nerves) arise from the brainstem.
• CN-II is not a peripheral nerve in the strictest sense, but it is technically a component of the CNS. This is because it is a rather a tract which outpouches from the diencephalon during embryonic development.

• CN 0 – Terminal
• CN I – Olfactory
• CN II – Optic
• CN III – Oculomotor
• CN IV – Trochlear
• CN V – Trigeminal
• CN VI – Abducens
• CN VII – Facial
• CN VIII – Vestibulocochlear
• CN IX – Glossopharyngeal
• CN X – Vagus
• CN XI – Accessory
• CN XII – Hypoglossal

Pathology

• Cranial nerve diseases

 

Compare with

• Spinal nerves

Cranial Nerve I: Olfactory Nerve

Organ system: The cranial nerves

Functions

Sensory

• Olfactory sensation from the nostrils in the nose.

Cranial Nerve II: Optic Nerve

Organ system: The cranial nerves

Functions

Sensory

• Vision sensation from the retina in the eye.  

Cranial Nerve III: Oculomotor Nerve

Organ system: The cranial nerves

Function

Motor

• Carries motor signals to the iris. This is an intraocular muscle which constricts the pupil.
• Carries motor signals to several extraocular muscles. These can draw the pupil of the eye upwards, downwards or inwards.

Cranial Nerve X: Vagus Nerve

Organ system: The cranial nerves

Structure

• The vagus nerve has a very long path through the body, reaching as far as the transverse colon.

 

Functions

Autonomic

• Carries parasympathetic signals between the CNS and most of the body. At the level of the pelvis, parasympathetic functions are mediated by the pelvic splanchnic nerves instead.
• In particular, the vagus nerve promotes gastrointestinal activity. 
• As vagal tone increases, the heart rate and stroke volume decrease.

Motor

• Motor output to the palatoglossus muscles.
• Motor output during swallowing (alongside CN-IX and CN-XII).
• Motor output during the pharyngeal (gag) reflex.

 

Pathology

• Peptic ulcer disease: The vagus nerve stimulates gastrointestinal acid secretion, and therefore contributes to gastrointestinal ulceration.
• Autonomic dysfunction in spinal cord injury: The sympathetic nervous system transmits signals through the spinal nerves and therefore cannot function after a severe spinal cord injury. The vagus nerve leaves the brain, not the spinal cord, and continues to function despite any spinal cord injuries. This leaves the parasympathetic output is unopposed and can cause life-threatening hypotension.
• Vagotomy: Surgical or traumatic removal of the vagus nerve reduces parasympathetic output to most of the body.